Disclaimers: JKR still owns it all. I write AU/OOC...if you want canon you picked the wrong story.
Dear Doctor Ruth...
Our story begins as Narcissa Malfoy had to enter the Hogwarts Express in search of her son who had not disembarked from it in a timely manner. She found her son and his two goons in a sorry state of health and in definite need of medical attention. Since she had no doubts what-so-ever that their physical conditions were the results of their own idiocy she reckoned that it was time for her to step in and assume the mantle of Malfoy Regent. And, things were going to be done her way!
She levitated all three boys off the train but left the two henchmen lying on the platform. If their parents were smart enough to recognize their children- Good. If not, too bad! Her son she would take home and begin to rehabilitate immediately. The Malfoy stupidity could no longer be left unchecked to run rampant. She would do what she had to to save her only child from both her husband and the idiot he served.
And so the plot thickens...
Narcissa Malfoy was just about as pleased as a woman could be when the Mediwizard she called in to attend her son rose from his position beside Draco's bed and announced, "Madame, I have done all I can do for your child. Most of the spells which hit him have been reversed or cancelled. However, there is one spell which I have not been able to dispel."
The aristocratic blonde spoke gently so as not to spook the healer, "What spell were you not able to dispel?"
"Someone seems to have hit him with the Veela Charm. Nothing I tried seems to be working."
"Not to worry. There are the occasional Veela genes in both my husband's and my family trees."
The healer blanched. "Oh! This is terribly unfortunate news!"
"Why so?"
"Because the reversal spell cannot cancel the true appearance of the gene itself. It could, however, cause the victim to become gender confused..."
Narcissa threw back her head and laughed delightedly. Her blue eyes, normally so cold and calculating, flashed with pleasure.
The healer, well used to the eccentricies of the aristocracy, was not too worried. "I will leave a few calming draughts with you in case they are needed, yes?" It was obvious that the man thought Narcissa was overwrought regarding the situation.
She still had a small case of the giggles as she rose gracefully from the edge of the settee that she had the house elf move into Draco's room for her while the healer worked on restoring him to health. After escorting the healer back to the floo room and thanking him once again for his prompt and valuable service, she waited until he had flooed away and broke out in the most evil cackle heard at Malfoy Manor in several decades.
Then rubbing her hands together gleefully as she acknowledged the coming together of a perfect plan, she headed back upstairs to her once-son's room. The world need never know that it was Narcissa Malfoy herself that cast the curse on Draco that activated his Veela gene...